Electrostatic printing apparatus



Nov. 30, 1965 P. A. STOWELL 3,220,303

ELECTROSTATIC PRINTING APPARATUS Filed Feb. 8, 1962 FIGZ INVENTOR. PHILIP A. STOWELL AGENT United States Patent 3,220,303 iiriscrnosrarrc PRlN'lilNG APPARATUS Philip A. Stowell, Paoli, Pa, assignor to Bnrrough Corpo- This invention relates to electrostatic printing apparatus and more particularly, although not necessarily exclusively, to electrostatic printing apparatus of the type wherein an electrostatic image pattern is produced on a recording medium without employing a conductive backing material for such medium in a manner permitting the image to be viewed by reflected or projected light, as for example, where the recording medium is a transparent or translucent film, strip or sheet.

In Campbell et al., Serial No. 814,055, filed May 18, 1959, now US. Patent No. 3,076,393 for an Electrostatic Page Printer, assigned to a common assignee, there is described a printing process wherein a record is first produced comprising latent electrostatic images of the characters of the text printed serially in a longitudinal direction on a continuous elongated light-permeable member or translucent tape. After this initial record is inked with a suitable powder to render the characters visible and opaque, the ultimate record is made on a medium preferably of page width and at a line at a time, by reproducing successive portions of the tap-e record.

Generally, such prior art electrostatic printing mediums have comprised a relatively thin, high dielectric film laminated or otherwise applied to conductive base supporting materials, such for example, as conductive paper or metal foil. This requirement results from the necessity for providing an electrically conductive path up to the back side surface of the dielectric material through which electrons may flow during the printing and inking steps, respectively, first to establish, and then to partially discharge an image pattern on the conductor-dielectric interface opposite the primary charge pattern which has been deposited on the top or upper surface of the dielectric. The closeness of the electrostatic image charge pattern to the prime charge pattern which is thus affordedthe separation between the two being only equal to the thickness of the dielectric filmresults in a very high effective capacitance between the two and, for a given potential difference between them, a very large amount of charge will be stored per unit area on the charge pattern, i.e., for a given high charge density the potential difference between the prime and image charges will be relatively low. The significance of this is that a high storage charge density is necessary in order that the inking operation will result in a dense, strongly adherent deposit of ink particles on the pattern, which is desirable for copy of highly readable quality. But for this, if a comparable amount of charge were deposited in a low capacitance medium, the image potential would, as aforementioned, be very high, as a result of which electrical breakdown of the image to the surrounding air and laterally across the dielectric surface surrounding the image would result, with a consequent decline of image charge density to an undesirably low level and a concomitant spreading and blurring of the image pattern.

Thus, in view of the foregoing, it can be seen that there is a requirement in the prior art printing apparatus to provide a conductive supporting medium, and such medium whether paper, foil or a conductive coating of some kind, is relatively more costly than many non-conducting supporting media, including non-conducting paper, that might otherwise be used strictly on the basis 3,220,303 Patented Nov. 30, 1965 ice of mechanical, esthetic, or economic considerations, Also, if a requirement for transparency or even a high degree of translucency exists, it is not possible to meet it with any practical supporting media. Dielectric films which are transparent are, on the other hand, readily obtainable. Therefore the elimination of the requirement of a conductive, supporting material for the electrostatic printing medium will at once remove both limitations.

It is a primary and important object of the present invention therefore to provide electrostatic printing apparatus for producing electrostatic image patterns on recording media having no conductive backing thereon.

Another object of the invention is to provide electrostatic printing apparatus for producing electrostatic image patterns on transparent recording media.

It is a further object of the invention to provide electrostatic printing apparatus wherein a temporary conductive backing member is provided for the recording media which may be an integral part of the printer.

It is also an object of the invention to provide electrostatic printing apparatus for producing visible electrostatically formed images on a continuous transparent recording medium for instantaneous projection and/or viewing.

In accordance with the foregoing objects, and first briefly described herein, the present invention comprises electrostatic printing apparatus including a conductive platen member maintained at reference ground or chassis potential across which a transparent recording medium such as a dielectric film, tape or sheet is moved ina continuous sliding or rolling contact past an electrostatic image forming transducer to an inking member for producing a visible pattern thereon and wherein the platen provides a temporary conductive backing member for such record medium supplanting the conductive backing and supporting member usually associated with electrostatic record media. Thereafter the inked image is fixed as by heat and/ or applied pressure.

In accordance with another feature of the invention there is provided a plurality of paraxially stacked tangentially disposed driving rollers operable alternately in opposite directions and 'over which the dielectric film or sheet is threaded or wound. At least the first one of the rollers is conductive and is maintained at ground or chassis potential. An electrostatic image is formed and inked into a visible pattern at this roller. The second roller is an idler roller. Fixing by heat and/ or pressure is performed between the third and fourth rollers. In this arrangement the first roller provides a temporary conductive backing member formerly provided 'by the conductive backing material usually bonded or otherwise secured to the electrostatic printing medium.

For a better understanding of the present invention together with other and further objects thereof, reference may now be had to the following description taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a diagrammatic view of one embodiment of the present invention;

FIG. 2 is a diagrammatic view of another embodiment of the present invention utilizing a plurality of paraxially stacked rollers;

FIG. 3 is a view of a further embodiment of the invention utilizing two conductive rollers; and,

FIG. 4 is a diagrammatic view of projection apparatus embodying the present invention.

Reference is now had to the drawings wherein various figures will be discussed more or less concurrently. The present invention solves the problem of electrostatic printing on dielectric media which is not conductively backed, e.g., laminated to, or in contact with a conductive backing member such, for example, as conductive paper, etc. In

electrostatic printing there is a requirement that there be conductivity to the back side or under surface of the dielectric during printing and later during inking, so that electrical charges may fiow first to and then away from the underside of the dielectric thereby to establish an image charge which is substantially equal to and identical in shape to the image which has been produced on the top of the dielectric. By providing electrostatic recording media such as paper with an electrostatically conductive backing or underlay, these charges are able to flow to and from the dielectric. Conversely, if the backing material is non-conductive, electrostatic printing is generallynot possible.

It has been and still is very desirable to employ a transparent medium as the electrostatic image pattern receiving member. Unfortunately, however, no known good conductors are transparent. The best conductors are metallic or carbonaceous. However, it has been found experimentally that it is not necessary, after the electrostatic image charge pattern has been formed and inked, to have the conductivity between the backing member and the surface of the conductor of the dielectric.

To this end the present invention as set forth in the embodiment of FIG. 1, employs a platen member 10, which as shown is a slightly, radially curved conductor divided into two similarly shaped though oppositely disposed or oriented parts a and 10b, for purposes to be explained presently. Conductor 10A is electricaly maintained at ground or chassis potential, as indicated by the ground connection 12. Across the radial surface 14 of the member 10 to a dielectric record medium 16 such as a tape, film or page is transported by means including the guide and drive rollers 17 and 17' respectively, in sliding or rolling contact therewith. In this manner platen member 10 is effectively in contact with the metal chassis of the printer or it may be integral therewith so as to provide a temporary electrical conductor at the underside 18 of the dielectric film 16 long enough for printing and inking to be accomplished, as hereinafter described.

The material forming the record medium 16 should preerably be a good dielectric, i.e., a material, the volume resistivity of which is not less than 10 ohm-centimeters and whose surface is non-hygroscopic, e.g., polyethylene coated cellophane for a transparent medium or polyethylene coated rag tissue for a reasonably translucent medium to which a dielectric coating has bene applied. The surface of the platen 10 is curved so that the dielectric record film or strip 16 may be streached taut thereacross thus to exclude any substantial air film from beneath the dielectric. In operation the tape is transported by means aforementioned, first to an electrostatic transducer 20, energized over cable 22, from a source of information signals, in a manner similar to that shown and described in Patent No. 2,919,170 of Herman Epstein, issued December 29, 1959 for Means For Electrostatically Recording Signals assigned to the same assignee as the present invention, and thence to an electrostatic inker 24 of conventional design whereby a latent electrostatic image charge pattern is formed and inking thereof can occur successively while the dielectric medium 16 is in motion and in contact with the platen 10. The record medium then passes to a fixing station 26 which may be of the electrical resistance or radiant heater variety energized over the leads 28 in conventional fashion. The rollers 1717' may be of hardened steel so as to provide a high calendering pressure for fixing.

In electrostatic printing apparatus of the foregoing type wherein heat fixing is employed problems may arise due to heat fiow back from the fixer 28 to the printing and inking devices and 24. This may manifest itself at the inking station 24 since the metal platen 10 will be heated by the fixer and the thermoplastic ink softened to the extent that it may have considerable tendency to agglomerate or to adhere to the dielectric material 16, causing it to flow slightly blurring the image pattern.

To avoid this condition or at least reduce the heat flow effects to a minimum, the member 10 is or may be made discontinuous, as shown. The two separate portions 10a and ltlb may then be positioned closely adjacent one another as indicated by the reference character 30 thereby providing a substantially continuous supporting surface for the record member 16 while at the same time preventing reverse heat flow from the fixing station 26 back to the inking station 24.

A more sophisticated means for offsetting certain of the problems associated with the curved platen arrangement of FIG. 1 is set forth in the embodiment of FIG. 2 which is seen to have a plurality of rigid conductive rollers 34, 36 and 38 together with a dielectric roller 40. The rollers are disposed paraxially and in close tangency to each other with the dielectric recording member 16 being threaded back and forth around the first and over the next and so on, alternating in direction as it passes from one roller to another. Rollers 34, 36 and 38 and 40 are driven in a conventional manner by means not shown.

With the foregoing apparatus the dielectric record medium 16 e.g., polyethylene coated cellophane is provided with an electrostatic charge pattern at 42 on opposite sides of the member 16 and inked at 44 against the outside of the dielectric in rolling contact with roller 34. Roller 34, maintained at ground potential provides a temporary conductive backing member for the dielectric record medium. This arrangement enables the dielectric to discharge the underside or image charge thereby permitting this image charge to flow into the ink. Thereafter the dielectric is fed around roller 36 in the opposite direction to that of roller 34 so that the image pattern which was on the out side of the first roller 34 and which was printed and inked thereat, now passes around the second roller 36 on the opposite side against the roller. Thereafter as the di electric 16 passes away from roller 36, around the third roller 38, the image pattern will again be on the outside. Roller 38 is heated by means for example, of resistance elements 46 which may be energized through sliding contacts from a suitable source of potential designated V. The dielectric 16 is then passed between the thus heated calendering roller 38 and the dielectric roller 40 wherein fixing can occur as desired. It is apparent that roller 40 need not be of dielectric material and in fact for pressure fixing would be of a hard metal.

The apparatus of the embodiment of FIG. 2 utilizing four successive rollers operating tangentially enables electrostatic printing to be accomplished on a dielectric film, transparent or opaque, which is unbacked by any conductive layer, metallic, carbonaceous, conductive paper, etc. "With such apparatus it is also possible to print on ordinary paper having a dielectric coating thereon which has not heretofore produced good electrostatic printing, because the base paper sheet was non-conductive. However, it has been discovered that if the paper is made thin enough, printing by this technique can nevertheless occur because the capacitance between the dielectric and the platen or roller beneath the paper provides a temporary conductive backup member for the formation of a satisfactorily strong electrostatic image charge on the record medium. For the best printing the magnitude of the thickness of the record medium, e.g., paper should not be more than a few times the thickness of the dielectric itself. Adequate printing has been accomplished utilizing paper that was one to one and onehalf mils thick. Sample mediums have included polyethylene coated cellophane film which provided adequate printing since polyethylene provides an excellent dielectrio. Good printing has also been accomplished with paper of tissue weight of the type ordinarily used as carbon copy paper in typing coated with a polyethylene dielectric.

As still another alternative, an arrangement is illustrated in FIG. 3 wherein calendering pressure provided between the two rollers 48 and 50 causes, for example, a

thermoplastic resinous ink forming the image charge pattern to be slightly softened and deformed and driven into the chemically similar surface of the dielectric thus to molecularly bond it to this surface by a technique much like that set forth in the copending application in the name of Philip A. Stowell, Serial No. 155,712, filed November 29, 1961, entitled Method For Fixing Electrostatically Printed or Formed Images Without Heat, assigned to the same assignee as the present invention.

Since it has now been demonstrated that a conductive backing member as such is not required to be aflixed to the record medium in order to effectively electrostatically form an image pattern or ink such pattern, it is readily apparent that transparent media formerly not usable with electrostatic printing may be employed.

Non-conductive transparent cellophane provided with a polyethylene dielectric coating can now be used as shown in FIG. 4. In this embodiment of the invention the dielectric coated cellophane 52 which is illustrated as a tape, but just as simply could be a page or sheet of material, is provided with an electrostatic image pattern 54, such for example, as weather information, including the usual barometric pressure, the altimeter setting, temperature, etc., in the manner and by means previously set forth herein in connection with the description of FIGS. 1, 2 and 3 of the drawings. By means of suitably positioned and oriented drive and guide rollers 56 and 58, operating at a desired speed and in the required direction, the dielectric 52 is fed before an optical system of conventional design which may include a light source 59, a condenser 60 and a focusing lens 62 whereby an enlarged image 64 is projected from the transparent film to a screen 66 or other image receiving member, e.g., a map of the area to which the weather report information is applicable or a stock market board on which changing stock quotations may be developed.

Unlike photographic apparatus, e.g., film and/ or printing material, the present invention can be made to provide a continuous recording-projecting-viewing system, by simply coupling the optical projection system to the electrostatic image pattern forming mechanism. In this manner the dielectric 16 coming away from the uppermost roller 40 in FIG. 2 could be passed immediately to the projection system shown in FIG. 4 to thereby provide substantially instantaneous recording and viewing of the desired information.

There has thus been disclosed a novel electrostatic printing apparatus wherein clean, clear, sharp and distinct electrostatically formed opaque image patterns are produced on transparent record media by means of apparatus providing a continuous electrically conductive path for the image charges applied to the record medium in the area including the electrostatic transducer and the inking mechanism. Such apparatus may comprise a separate conductive member extending from the transducer to the inker or other means such as a roller electrically maintained at ground potential over which the record medium may be transported in surface contact therewith from the transducer forming the image charge pattern to the inker for rendering the charge pattern visible.

What is claimed is:

1. Electrostatic print-ing apparatus comprising, combination,

(a) a plurality of electrically conductive paraxially stacked tangentially arranged rollers,

(b) means maintaining a first one of said rollers at ground potential,

(c) an electrically energizable electrostatic image pattern forming transducer for applying a latent electrostatic image to a record member disposed adjacent said first one of said rollers,

(d) and an electrostatic inking member for applying ink to said record member to thereby produce a visible, viewable image thereon disposed adjacent said electrostatic transducer and in continuous relationship with said first conductive roller, said electrically conductive roller forming a conductive backing member over which said record member is adapted to be transported when said rollers are rotated in suitable directions.

2. Electrostatic printing apparatus comprising, in combination,

(a) an electrically energizable electrostatic image pattern forming transducer for applying a latent electrostatic image to a transparent record member,

(b) an electrostatic inking member for applying ink to said record member thus to produce a visible image thereon,

(c) an electrically conductive backing member adjacent the path of movement of said record member extending at least from said transducer to said inking member thereby to provide an electrically conductive supporting under surface for said record member,

((1) a thermal fixing member disposed in the path of movement of said record member adjacent said electrically conductive supporting under surface,

(e) and means for transporting the transparent record medium across and in surface contact with said electrically conductive supporting under surface thus to produce an electrostatic image charge pattern on said record member.

3. Electrostatic recording and printing apparatus for electrostatic printing of intelligible characters on record 30 mediums comprising in combination,

(a) means for electrostatically charging discrete areas of a transparent record member thereby to provide latent images-thereon,

(b) means for rendering the latent electrostatically charged areas visible by subjecting the transparent member to inking material,

(c) electrically conductive means maintained at ground potential,

((1) means for moving said record member over said conductive means during the charging and inking of said member whereby the inking material is attracted by and adheres to the electrostatically charged areas on the record member,

(e) means for fixing the inked images to said transparent member while said transparent member is in contact with said electrically conductive means,

(f) and optical projection means to which said record medium is passed, including means for projecting an image from said transparent member to a light reflective surface whereby the image may be viewed in ambient light,

4. Electrostatic printing apparatus comprising in combination,

(a) an electrically energizable electrostatic image pattern forming transducer for applying a latent electrostatic image to a record member,

(b) an electrostatic inking member for applying electrostatic ink to said record member thus to produce a visible image thereon,

(c) a discontinuous electrically conductive backing member adjacent the path of movement of said record member,

(d) a portion of said backing member extending from said transducer to said inking member thereby providing a conductive supporting under surface for said record member,

(e) a thermal fixing member disposed in the path of said record member and adjacent said conductive supporting under surface,

(f) means for transporting a transparent record medium across and in surface contact with said conductive under surface whereby an electrostatic image charge pattern is formed on opposite sides of said record member as a result of electrostatic charges flowing from said transducer through said record member to said conductive supporting under surface bination,

(a) an'electrically energizable electrostatic image patenergization of said transducer electrostatic image charge patterns are formed on said record member, inked into a visible image at said inking member and thereafter fixed in a manner permitting said image to be handled, viewed and optically projected.

References Cited by the Examiner tern forming transducer for applying a latent electrostatic image to a record'member,

UNITED STATES PATENTS (b) an electrostatic inking member for applying ink 10 118 637 to said record member to produce a visible, viewable 2931688 4/1960 35 3 image thereon,

(c) an electrically conductive platen maintained at 3? X ground potential disposed adjacent the path of move- 3O08242 11/1961 1 118 6 ment of said record member, the surface of said 15 3012839 12/1961 a I n X platen over which said record member is moved 3023731 3/1962 i being radially curved throughout its length thereby 3050580 8/1962 providing an electrically conductive backing sur- 3051O44 8/1962 fi g s} 88 24 face for mm member 3:0711645' 1/1963 McNaney 95-1.? x

(d) a thermal fixing member likewise disposed in the 20 path of movement of said record member adjacent said backing surface,

(e) further means in said path of movement adjacent said fixing member having a radially curved surface over which said record member can be moved,

(f) and means for transporting a transparent dielectrically coated record member across and in surface contact with said conductive surf-ace whereby upon OTHER REFERENCES Magneto-Luminescent Device, IBM Technical Disclosure Bulletin, vol. 3 No. 2, July 1960, page 71, relied upon.

NORTON ANSHER, Primary Examiner.

EMIL G. ANDERSON, Examiner. 

1. ELECTROSTATIC PRINTING APPARATUS COMPRISING, IN COMBINATION, (A) A PLURALITY OF ELECTRICALLY CONDUCTIVE PARAXIALLY STACKED TANGENTIALLY ARRANGED ROLLERS, (B) MEANS MAINTAINING A FIRST ONE OF SAID ROLLERS AT GROUND POTENTIAL, (C) AN ELECTRICALLY ENERGIZABLE ELECTROSTATIC IMAE PATTERN FORMING TRANSDUCER FOR APPLYIN A LATENT ELECTROSTATIC IMAGE TO A RECORD MEMBER DISPOSED ADJACENT SAID FIRST ONE OF SAID ROLLERS, (D) AND AN ELECTROSTATIC INKING MEMBER FOR APPLYIN INK TO SAID RECORD MEMBER TO THEREBY PRODUCE A VISIBLE, VIEWABLE IMAE THEREON DISPOSED ADJACENT SAID ELECTROSTATIC TRANSDUCER AND IN CONTINUOUS RELATIONSHIP WITH SAID FIRST CONDUCTIVE ROLLER, SAID ELECTRICALLY CONDUCTIVE ROLLER FORMING A CONDUCTIVE BACKIN MEMBER OVER WHICH SAID RECORD MEMBER IS ADAPTED TO BE TRANSPORTED WHEN SAID ROLLERS ARE ROTATED IN SUITABLE DIRECTIONS. 